[Morgeruat]

no they can't, but if you have a weapon such as rapier, or scimitar with a critical range of 18-20, get imp critical, and keen your critical range is 12-20 (if you add sharpness, or vorpal... ouch) meaning a critical hit on 45% of all swings (provided they hit), with vorpal added everytime you get a critical the target loses it's head, unless immune to vorpal)

Holy Avengers are minor affects for weapons, unless you have at least 1 paladin level, in which case they act as a normal holy avenger from PnP (carsomyr from bg2 is a fair, but by no means erfect, example of a holy avenger as far as powers and abilities.